In some kinds of vehicles and more especially utility and commercial vehicles, farm vehicles and the like, there is a need to provide a safety arrangement to prevent a given operating device of the vehicle from being brought into operation unless certain conditions for actuation thereof are met. Such a vehicle may be for example a tractor, a mowing machine, a fork lift truck, a lawnmower or the like. In the case of such vehicles, it is often important that an operating device thereof which may be for example a mowing mechanism, an output drive shaft, a lifting assembly or the like, can be activated or brought into operation only when the person for operating the vehicle has taken up the appropriate position on the driving seat of the vehicle. Thus, in order to ensure, in relation to such vehicles, that the source of danger to the person operating the vehicle, which is constituted by the operating device thereof such as the mowing mechanism, cannot come into operation under circumstances such that the operator is likely to be endangered thereby, such a vehicle or the operating device thereof, which constitutes the danger to the operator, is prevented from being actuated unless the operator is sitting on the vehicle seat for operating same. To achieve that aim, the seat plate or seat base of the vehicle seat may comprise a base portion and a seat cushion which is disposed thereon, and, between the base portion and the seat cushion, a switching device for switching on an electrical circuit of the operating device of the vehicle, when the seat base is subjected to a certain minimum weight loading, with the electrical circuit being switched off when there is no loading applied to the seat base. However, it has been found that the switching device has a tendency to operate reliably only when the operator is in the correct sitting position on the seat, more specifically the operator has assumed such a position that he occupies at least a substantial part of the top surface of the seat cushion and thus applies a pressure, by virtue of body weight, over a considerable part of the seat surface. In the case of utility vehicles for example in the form of a mowing machine however it may frequently happen that the driver does not sit fully on the driving seat in such a way as to cover substantially the entire seating surface thereof, but only sits on the seat base at the front edge thereof so that he can more closely observe the area directly in front of the vehicle. When the operator is in that position it has been repeatedly found, with previous designs of safety arrangement for the seat base for the operator seat of a utility vehicle, that the switching device disposed between the base portion of the seat and the seat cushion does not operate correctly and the operating device of the vehicle is switched off as a result, under circumstances in which that is not required.